1. Field of the Invention
The present invention is in the field of soft magnetic material suitable for use in magnetic recording heads consisting of a cobalt base amorphous material containing from 4 to 8 atomic percent of hafnium and 0.5 to 15 atomic percent of palladium. This material has a higher saturation magnetic flux density Bs and lower saturation magnetostriction .lambda.s.
2. Description of the Prior Art
In the field of magnetic recording, the tendency is towards increasing the density and the frequency of the recording signals, as evidenced by the perpendicular magnetic recording system. For use therewith, magnetic tapes having high residual magnetic flux density Br or a high coercive force Hc, such as metal powder tapes in which powders of ferromagnetic metals such as Fe, Co or Ni are used as magnetic powders or evaporated tapes in which a ferromagnetic metal material is evaporated on the base film have been suggested. The material of the magnetic head used for recording and/or reproduction of this type of magnetic recording medium must be large in saturation magnetic flux density Bs and magnetic permeability and hence must be lower in its saturation magnetostriction constant .lambda.s.
In any high density magnetic recording system, the recording track of the magnetic recording medium tends to be quite narrow. Thus, the recording track of the magnetic head must also be narrow in width.
It has previously been suggested to provide a so-called composite magnetic head in which an insulating layer and a soft magnetic thin film adapted to serve as the magnetic core are alternately disposed on a non-magnetic base such as a ceramic, or to provide a thin film magnetic head in which soft magnetic films and thin conductive films are arranged in a multi-layer structure using intermediate insulating layers. Recently, amorphous soft magnetic films have been developed for use with this type, of magnetic head.
These amorphous soft magnetic films are known to have a number of advantages such as near-zero magnetostriction, a higher magnetic permeability, and freedom from crystal magnetic anisotropy, and are highly useful as soft magnetic thin films for such magnetic heads.
It is known to make up amorphous soft magnetic thin films using metal-metalloid systems containing metalloid elements in addition to metal elements such as Fe, Ni and Co. It is difficult, however, with the metal-metalloid amorphous alloys to secure a predetermined saturation magnetic flux density Bs. For example, in a perpendicular magnetic recording single pole head, when it is desired to reduce the main magnetic pole film thickness to less than 3000 .ANG., the soft magnetic thin film making up the main magnetic pole must have a saturation magnetic flux density Bs higher than about 14000 Gauss. The saturation magnetic flux density Bs of the above described metal-metalloid amorphous alloy, however, is only on the order of 10000 Gauss.
Metal-metal amorphous alloys of the Co-Zr and Co-Hf series have recently evolved as amorphous alloys having a high saturation magnetic flux density. However, these metal-metal amorphous alloys while exhibiting an extremely high saturation magnetic flux density on the order of 15000 Gauss for a Zr or Hf ratio of about 5 atomic percent, have a large saturation magnetostriction constant on the order of +3.times.10.sup.-6. Therefore, the initial magnetic permeability is lower than about 2000 along the hard magnetization axis for the frequency range of 1 to 10 MHz. The published, unexamined Japanese Patent Application No. 207308/82 laid open to the public on Dec. 20, 1984 describes such a cobalt-hafnium amorphous soft magnetic film.
There has also been suggested a Co-Zr-Nb amorphous alloy in which Nb is added to the aforementioned composition for reducing the saturation magnetostriction constant .lambda.s. For example, with a Co percentage of 93 atomic percent at most, and a ratio of Zr:Nb equal to 3:5, the amorphous alloy has a saturation magnetostriction constant .lambda.s equal to zero and an initial magnetic permeability higher than 3000 along the hard magnetization axis for the frequency range of 1 to 10 MHz. The alloys thus exhibit acceptable soft magnetic properties. However, the saturation magnetic flux density Bs of these materials is less than about 14000 Gauss.
In summary, there has not been developed a soft magnetic thin film satisfying the requirements for both the saturation magnetic flux density Bs and the saturation magnetostriction constant .lambda.s.
It has been suggested in our prior Japanese Patent Application No. 95302/1984 to use a Co-Hf-Pt amorphous soft magnetic thin film wherein the saturation magnetic flux density Bs is higher than 14000 Gauss and the saturation magnetostriction constant .lambda.s is less than +1.5.times.10.sup.-6. However, to realize a saturation magnetic flux density Bs higher than 15000 Gauss and a saturation magnetostriction constant .lambda.s less than +1.5.times.10.sup.-6, the compositional range for which these two requirements are simultaneously satisfied is very narrow.